Strapping devices are used to wrap piles of boxes in a truck, for example, tightly so that the piles of boxes are maintained in a stable status which is benefit when transportation. In order to ensure the piles of boxes will not fall downwardly when the strap is loosened, the operators have to check the piles of boxes to prevent the higher portion of the piles of boxes from suddenly falling to injure the operators so that the conventional strapping devices are developed to have the function of loosening the strap slightly and still holding the boxes if the strapping devices are not operated to loosen the straps completely. Two known strapping device having such function are disclosed applicant's U.S. Pat. No. 5,778,496 issued on Jul. 14, 1998 and U.S. patent application Ser. No. 08/901,758, filed on Jul. 28, 1997 which is under the procedure of issuance. Both the two strapping devices resolve the problems described above, However, a movable frame in each of the two strapping devices is pulled by springs so that once the force of the strap is disappeared, the frame will be pulled backward quickly without any warning. The hand of an operator having no long-term experience could be clamped by the sudden moving frame.
The present invention provides a strap tightening/loosening device having a limit member which is disengaged with the movable rod of the frame which is not pulled by springs so that the frame will not injure the operators when the strap is completely loosened.